fix: Path traversal in view_issue_raw_file()
Use 'werkzeug.security.safe_join()' instead of plain 'os.path.join()'
to sanitize user-provided filename variable and avoid escaping the base directory.
Vulnerability discovered by Thomas Chauchefoin <thomas@chauchefoin.fr>
Fixes: rhbz#2279411, rhbz#2280728, rhbz#2280726, CVE-2024-4982
Signed-off-by: Dominik Wombacher <dominik@wombacher.cc>